Human colonic intraepithelial lymphocytes suppress in vitro immunoglobulin synthesis by autologous peripheral blood lymphocytes and lamina propria lymphocytes

Human colonic intraepithelial lymphocytes regulate the cytokines produced by lamina propria mononuclear cells

Using an in vitro autologous human system, the immunomodulatory function of colonic intraepithelial lymphocytes (IEL) on cytokine production by lamina propria mononuclear cells (LPMNC) has been investigated. In contrast to LPMNC, colonic IEL produced only low amounts of IL-10, interferon-gamma and interleukin-2. However, co-culture experiments (IEL + LPMNC) have shown that IEL can enhance the PHA-induced synthesis of IL-2 and interferon-gamma, but not IL-10 by LPMNC. Using a transwell filter culture system apparatus, this effect was shown not to require a cell-to-cell interaction. Thus, IEL in vitro may modulate the cytokine synthesis of LPMNC, through the production of soluble factors. This may prove highly relevant in the in vivo immune activation of the gastrointestinal mucosa.

Human small-intestinal epithelium contains functional natural killer lymphocytes

BACKGROUND & AIMS

CD3(-) non-T lymphocytes constitute the second most abundant lymphoid subset in the human small-bowel epithelium, and these CD3(-) intraepithelial lymphocytes are virtually absent in active celiac disease. Phenotypically, they resemble natural killer cells and have been termed natural killer-like intraepithelial lymphocytes. Because of the limited availability of appropriate human samples, functional studies have not yet been reported, and it is not yet clear whether these are true natural killer cells.

METHODS

We used magnetic bead-based purification and flow cytometry to study several aspects of normal human small-bowel natural killer-like intraepithelial lymphocytes: intracellular cytokine content (basally and after activation); ability to lyse natural killer-sensitive K562 target cells; and expression of perforins, Fas ligand, and other functional markers.

RESULTS

CD3(-) intraepithelial lymphocytes cultured in interleukin-2 showed a higher lymphokine-activated killer activity than CD3(+) intraepithelial lymphocytes (48%-83% lysis exerted by CD3(-) intraepithelial lymphocytes at an effector-target cell ratio of 2:1 vs. 8%-18% by CD3(+) intraepithelial lymphocytes). Perforin content correlated with this lytic potential (75% +/- 4% in CD3(-) vs. 5% +/- 4% in CD3(+) intraepithelial lymphocytes). Both CD3(-) and CD3(+) cells displayed a type I cytokine profile (interferon-gamma > tumor necrosis factor-alpha > interleukin-2; undetectable interleukin-4 and interleukin-10). In addition to their activated phenotype, subsets of natural killer-like intraepithelial lymphocytes expressed CD8alphaalpha and intracellular CD3epsilon chain, showing the existence of heterogeneity within this cell lineage.

CONCLUSIONS

This is the first demonstration of functional natural killer cells within the human gut epithelium. These cells might play an important role in innate mucosal immunity (host defense and tumor surveillance) and tolerance.

Current understanding of gastrointestinal immunoregulation and its relation to food allergy

Tolerance to food antigens induced via the gut ("oral tolerance") appears to be a rather robust adaptive immune mechanism. However, the neonatal period is particularly critical in terms of mucosal defense, with regard to infections and priming for allergic disease. This is so because the intestinal barrier function provided by secretory antibodies, as well as the immunoregulatory network, is poorly developed for a variable period after birth. Notably, the postnatal development of mucosal immune homeostasis depends on the establishment of a normal commensal microbial flora and also on adequate timing and dose of dietary antigens when first introduced. In this context, breastfeeding appears to exert both shielding and positive regulatory effects. Altogether, the intestinal immune system normally seems rather fit for tolerance induction against innocuous antigens because most children with food allergy "outgrow" their problems, whereas airway allergy tends to persist.

Advances in mucosal immunology

HIV infection is likely to remain a significant medical and scientific problem well into the twenty-first century. During the first 15 years of the epidemic, much has been learned about the biology of HIV infection, but the majority of biomedical research has focused on the peripheral circulation. It is likely that the behavior of the virus within the unique immunologic environment of the intestinal mucosa differs from that which is observed in the periphery. Many clinical and epidemiologic features of HIV infection offer compelling reasons to encourage further examination of the mucosal immune system's role in AIDS pathogenesis. This article has touched on most of the significant observations concerning the mucosal immune system and HIV infection, and it is clear that much remains to be done. As mentioned earlier, the mucosal abnormalities observed in HIV infection are likely to have many causes. Careful evaluation of patients with early disease and fewer confounding variables may provide fresh insight into AIDS pathogenesis. Similarly, prospective evaluation of selected patient populations may be more informative in characterizing the progressive alterations in mucosal immune function than random cross-sectional studies of poorly defined groups. It is equally important for immunologic assessment to be correlated with nutritional and symptomatic evaluation. Finally, the success or failure of future antiretroviral therapies will be critically related to the impact of such agents on lymphoid reservoirs of HIV infection such as the gastrointestinal tract, which are at present refractory to treatment.

Intestinal intraepithelial lymphocytes influence the production of somatostatin

BACKGROUND

We have previously demonstrated that intestinal intraepithelial lymphocytes (iIELs) inhibit lymphocyte proliferation. Because somatostatin also prevents lymphocyte proliferation, we hypothesized that iIELs may influence production of somatostatin.

METHODS

Isolates of intestinal epithelium that were obtained from Brown Norway (BN) rats and contained an iIEL-enriched population (defined as CD45+) were incubated with irradiated Lewis splenocytes for allogeneic stimulation. BN rat splenocytes incubated with irradiated Lewis splenocytes served as a control. Supernatants were harvested after 4 days and assayed for somatostatin by using a radioimmunoassay.

RESULTS

The somatostatin level in the intestinal epithelium-conditioned supernatant was significantly higher than that of the control group (176 +/- 60 versus 10 +/- 2 fmol/ml; p < 0.05). Removal of the CD45+ cell subset resulted in a fifteenfold reduction in somatostatin levels. The CD45+ cell lysates had significantly higher levels of somatostatin than did CD45+ depleted cells (1304 +/- 531 versus 128 +/- 41 fmol/ml; p < 0.05).

CONCLUSIONS

The isolates of intestinal epithelium produced significant amounts of somatostatin. Removal of the CD45+ cells caused a significant loss of somatostatin production. Intracellular levels of somatostatin appeared to be highest in the CD45+ subpopulation. These data suggest that iIELs (that is, CD45+ cells) may have a significant influence on the production of somatostatin and may be a source of somatostatin production. Production of somatostatin by iIELs may help modulate immune responses in gut-associated lymphoid tissue.

Mucosal enzyme activity for butyrate oxidation; no defect in patients with ulcerative colitis

BACKGROUND

Butyrate is an important energy source for the colon and its metabolism has been reported to be defective in ulcerative colitis. One mechanism for defective butyrate metabolism in patients with ulcerative colitis could be an enzyme deficiency in the beta-oxidation pathway of butyrate.

AIMS

This study was undertaken to measure the activity of each enzyme involved in the beta-oxidation pathway of butyrate in colonic epithelium.

PATIENTS

Patients with ulcerative colitis (n = 33), Crohn's colitis (n = 10), and control subjects with colorectal cancer or diverticular disease (n = 73) were studied.

METHODS

Analysis was carried out using fluorometric and spectrophotometric techniques on homogenised epithelial biopsy specimens.

RESULTS

Significantly increased butyryl CoA dehydrogenase activity was found in mucosa from patients with ulcerative colitis (33.2 (28.3, 38.1) mumol/g wet weight/min:mean (95% CI)) compared with activity in mucosa from control patients (24.3 (20.9, 27.7) mumol/g wet weight/min:mean (95% CI)) p < 0.02. No significant increase in activity of the enzymes butyryl-CoA synthetase, crotonase or hydroxybutyryl-CoA dehydrogenase was found in patients with ulcerative colitis. In contrast the mucosal thiolase activity was significantly lower in those patients with quiescent colitis (3.21 (2.61, 3.81) mumol/g wet weight/min:mean (95% CI)) when compared with control mucosa (5.69 (5.09, 6.29) mumol/g wet weight/min:mean (95% CI)) p < 0.001. However, mucosal thiolase activity increases with the age of the donor patient and differences in the age range of the patient groups probably account for this finding.

CONCLUSIONS

This study shows no substantial deficiency of enzyme activity in the beta-oxidation pathway of butyrate in the mucosa of patients with ulcerative colitis in histological remission.

Food antigen activates intraepithelial and lamina propria lymphocytes in food-sensitive enteropathy in mice

Morphologic and immunologic changes in the gut mucosa of food-hypersensitive mice, from a study model generated by feeding ovalbumin (OVA) to female BALB/c mice after intraperitoneal injection of cyclophosphamide (CY), were investigated in an effort to clarify the mechanisms of food-sensitive enteropathy. Villous atrophy, crypt hyperplasia, and increased numbers of intraepithelial lymphocytes (IEL) were confirmed in the antigen-challenged OVA-sensitive mice as seen in food-sensitive enteropathy in humans, whereas no significant morphologic changes were observed in the nontreated control group or groups treated with OVA or CY alone. IEL and lamina propria lymphocytes (LPL) were isolated from the intestinal mucosa before and after the antigen challenge, and surface markers were analyzed by FACScan. After the antigen challenge, the numbers of CD8+ cells increased among the IEL, and the occurrence of both CD4+ and CD8+ cells increased among the LPL. The numbers of Thy-1+ cells and TCR- alpha/beta + cells increased among both the IEL and LPL, and LFA-1 expression was enhanced in both of these lymphocyte populations. The proliferative response of IEL and LPL to OVA increased in a dose-dependent manner after the antigen challenge in the OVA-sensitive mouse model. These results indicate that IEL and LPL, possibly those that have migrated from peripheral blood, are activated by orally administered antigens and cause mucosal damage in the food-sensitive enteropathy.

History of oral tolerance and mucosal immunity

Mucosal immunity depends on antigen stimulation in specialized lymphoepithelial structures such as the Peyer's patches. Although these inductive compartments were discovered more than 300 years ago, their functional role has become clear only over the last few decades. Research on homing of primed lymphoid cells to the intestinal mucosa began with animal experimentation in the 1960s and 1970s and has recently been brought to the molecular level. The major effector substance of mucosal immunity is secretory IgA (SIgA). The first evidence for its local antibody activity was obtained in humans in 1922, but its unique properties were not defined until the mid-1960s. Several models were subsequently proposed for selective external transport of IgA involving the secretory component (SC). In the early 1970s SC was suggested to act as a transmembrane polymeric Ig receptor common for dimeric IgA and pentameric IgM; this transport mechanism has now been confirmed by detailed studies at the level of cellular/molecular biology. Although SIgA antibodies performing immune exclusion are the main goal for exploitation of the mucosal immune system by oral vaccination, little is known about the precise mechanisms for induction of mucosal immunity against soluble proteins and chemicals. A peripheral immunosuppressive effect of oral immunization with such substances was apparently exploited by ancient people, and "oral tolerance" has since 1910 been subjected to numerous feeding experiments in rodents. The basis for the whole phenomenon appears to be intact epithelial barrier. Mucosal induction of suppression may in the future be exploited not only to modulate autoimmune diseases through the gut but also to prevent the development of IgE-mediated allergy and other untoward immune reactions by way of the respiratory tract.